Implement six major improvements to typing tutor

1. Start in Adaptive Drill by default: App launches directly into a
   typing lesson instead of the menu screen.

2. Fix error tracking for backspaced corrections: Add typo_flags
   HashSet to LessonState that persists error positions through
   backspace. Errors at a position are counted even if corrected,
   matching keybr.com behavior. Multiple errors at the same position
   count as one.

3. Fix keyboard visualization with depressed keys: Enable crossterm
   keyboard enhancement flags for key Release events. Track depressed
   keys in a HashSet with 150ms fallback clearing. Depressed keys
   render with bright/bold styling at highest priority. Add compact
   keyboard mode for medium-width terminals.

4. Responsive UI for small terminals: Add LayoutTier enum (Wide >=100,
   Medium 60-99, Narrow <60 cols). Medium hides sidebar and shows
   compact stats header and compact keyboard. Narrow hides keyboard
   and progress bar entirely. Short terminals (<20 rows) also hide
   keyboard/progress.

5. Delete sessions from history: Add j/k row navigation in history
   tab, x/Delete to initiate deletion with y/n confirmation dialog.
   Full chronological replay rebuilds key_stats, letter_unlock,
   profile scoring, and streak tracking. Only adaptive sessions update
   key_stats/letter_unlock during rebuild. LessonResult now persists
   lesson_mode for correct replay gating.

6. Improved statistics display: Bordered summary table on dashboard,
   WPM bar graph using block characters (green above goal, red below),
   accuracy Braille trend chart, bordered history table with WPM goal
   indicators and selected-row highlighting, character speed
   distribution with time labels, keyboard accuracy heatmap with
   percentage text per key, worst accuracy keys panel, new 7-month
   activity calendar heatmap widget with theme-derived intensity
   colors, side-by-side panel layout for terminals >170 cols wide.

Also: ignore KeyEventKind::Repeat for typing input, clamp history
selection to visible 20-row range, and suppress dead_code warnings
on now-unused WpmChart.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/ui/components/stats_sidebar.rs

@@ -26,7 +26,7 @@ impl Widget for StatsSidebar<'_> {
         let accuracy = self.lesson.accuracy();
         let progress = self.lesson.progress() * 100.0;
         let correct = self.lesson.correct_count();
-        let incorrect = self.lesson.incorrect_count();
+        let incorrect = self.lesson.typo_count();
         let elapsed = self.lesson.elapsed_secs();
 
         let wpm_str = format!("{wpm:.0}");